Overall size is 6" x 6" (by 1" deep). The cubbies are bit under 2" x 2" (approx 1-7/8" square).
Also shown in one of the photos above with the Shadowbox with Square Cubbies - 8x8.
Laser-cut heavy chipboard. Ships flat but a breeze to put together with the slots and tabs precut (you'll just need to secure with a bit of white glue).GND gryGD